Not applicable.
1. Field of the Invention
The present invention relates to a pneumatically-operated reciprocating fluid pump and shuttle valve shifting mechanism, and more particularly relates to a pneumatically-operated reciprocating fluid pump that utilizes bleed pneumatic pressure from the supply fluid (typically compressed air) to shift the shuttle valve.
2. Description of the Prior Art
Pneumatically-actuated reciprocating pumps are well known in the fluid industry. Such reciprocating fluid pumps are operated by a shuttle valve which shifts pressurized air from one pneumatic chamber of the pneumatic reciprocating pump to the other as the pumping means (flexible diaphragm, piston, bellows, etc.) reaches the end of its pumping stroke. A valve spool in the shuttle valve shifts between two positions which alternately supply pressurized air to the pneumatic chamber of one side of the pump while simultaneously permitting the other pneumatic chamber to exhaust the air therefrom. Reciprocation of the valve spool alternates this pressurized air/exhaust between pairs of pneumatic chambers within the pneumatically-actuated reciprocating pump, thereby creating the reciprocating pumping action of the pump.
Most pneumatically-operated reciprocating fluid pumps are, in fact, dual reciprocating pumps, meaning that the pump incorporates two pumping means (diaphragm, etc) that reciprocate in a manner such that the intake (suction) stroke of one pumping means (flexible diaphragm) is the exhaust (pressure) stroke of the other pumping means. In this manner, the dual reciprocating action of the diaphragms, etc. pump liquid from a first pumping chamber as liquid is being drawn into the second pumping chamber, followed by the reverse action of the two diaphragms, which pumps liquid from the second pumping chamber while drawing liquid to be pumped into the first pumping chamber.
A common problem with these dual-reciprocating fluid pumps is that as the drive shaft connecting the two flexible diaphragms, and therefore the diaphragms themselves, reaches the end of its pumping stroke, the abrupt change (reversal) in direction of the drive shaft and diaphragms generates vibration of the pump. These repeated abrupt reversals of direction (in both directions) of the drive shaft and diaphragms not only vibrate the pump, connections, and fluid conduits within the system, they also prematurely destroy the diaphragm and drive shaft, necessitating frequent replacement of the diaphragms and drive shaft.
Prior art pneumatically-actuated reciprocating fluid pumps have also consistently had problems with pumped-fluid surge as pumped fluid from one pumping chamber abruptly stops and fluid from the opposite pumping chamber abruptly starts. This surge causes what is termed hydraulic hammering in supply lines that tends to vibrate the lines, resulting in unnecessary abrasion, flexure, and fatigue in the lines, and also tends to vibrate the fluid connections and fittings loose near the pump. In certain applications, surge can dislodge particulate contamination or other particulate matter from the pump construction material (e.g., Teflon) and introduce this contamination into the fluid system.
A pneumatically-shifted reciprocating fluid pump is shifted by a pneumatically-shifted shuttle valve, the shuttle valve being shifted to reciprocate the pumping means of the pump by reciprocating pneumatic pressure within the pump alternately between the two pneumatic chambers. The present invention extends the life of the flexible diaphragms and drive shaft by minimizing the effect of the drive shaft and diaphragms abruptly reversing direction as the drive shaft and diaphragms reach the end of their pumping stroke. It does this by xe2x80x9cstealingxe2x80x9d a blast of supply air from the pressurized pneumatic chamber to shift the shuttle valve to its opposite position to reverse the feed of pressurized air and exhaust to the two pneumatic chambers of the fluid pump. This xe2x80x9cstolenxe2x80x9d supply of pressurized air from the pressurized pneumatic chamber decreases the pressure in the pneumatic chamber, thereby decreasing the force applied to the drive shaft, causing the drive shaft and diaphragms to slow down as the drive shaft nears the end of its stroke, due to the pressure differential between the back pressure of the pumped fluid in the pressurized pumping chamber and the sudden decrease of pressure in the pneumatic chamber.
A valve mechanism is formed by the pump body and the drive shaft and connects the two diaphragms, etc. in their respective pneumatic chambers. This valve mechanism steals these blasts of compressed air supplied from the pressurized side of the pneumatic chamber and directs them to the appropriate end of the shuttle valve to shift the shuttle valve in the opposite direction. Specifically, the drive shaft includes two annular grooves that provide communication between the pressurized pneumatic chamber and the appropriate end of the shuttle valve as the drive shaft nears the end its stroke and the drive shaft annular groove passes over a drive shaft bore shift port and a shuttle valve shift port, establishing communication between the two. In this manner, as the drive shaft nears the end of its stroke, the pressurized pneumatic chamber is relieved of some of its pressure (this xe2x80x9crelievedxe2x80x9d pressurized air being used to shift the shuttle valve), thereby slightly reducing the pressure in the pressurized pneumatic chamber in order to decelerate the drive shaft, and therefore the two diaphragms, as the drive shaft and diaphragms approach the end of this pumping stroke half-cycle.
The reciprocating pump operates in an xe2x80x9cair-assistxe2x80x9d mode and a xe2x80x9cnon-air-assistxe2x80x9d mode. In the non-air-assist mode (as just described), the shuttle valve is shifted by a blast of pressurized supply air from the pneumatic chamber in its pumping stroke as the diaphragms and drive shaft reach the end of their pumping stroke. This blast of pressurized air used to shift the shuttle valve has the effect of reducing the air pressure in the pneumatic chamber immediately prior to the point in time that the drive shaft reaches the end of its stroke in order to provide a cushioning effect at the end of each pumping strokes cycle, in order to lessen the effect of the drive shaft and diaphragms abruptly reversing direction at full air pressure.
In the air-assist mode (in which higher sustained pumping pressures are required), shifting of the shuttle valve is provided by a separate xe2x80x9cair-assistxe2x80x9d. In this mode, a secondary source of compressed air is utilized to shift the shuttle valve, rather than drawing pressurized air from the pneumatic chamber during its pumping stroke. In the air-assist mode, full pressure air is available to pump fluid through the pump, and is not lessened by tapping a minute amount of compressed air at the end of each pumping stroke for shifting the shuttle valve. In addition, in the air-assist mode, the external pressurized air source can be at a much lower pressure than the pressurized air used to drive the pump, resulting in the use of a much smaller and/or less substantial (and therefore, less expensive) shuttle valve being useable in the system. Also, of course, running shuttle valves at lower operating pressures will prevent premature degradation of the valves themselves, as opposed to shuttle valves having to be run at the much higher pump-pressure. In the commercial embodiment of the fuel pump, shifting between the air-assist mode and non-air-assist mode is easily accomplished by switching a screw-plug between two designs for each fluid pump pneumatic chamber and providing the secondary air source for the shuttle valve shift air.